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.\" Copyright (c) 2010 Xin LI <delphij@FreeBSD.org>
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.Dd January 29, 2023
.Dt PTHREAD_ATTR_AFFINITY_NP 3
.Os
.Sh NAME
.Nm pthread_attr_getaffinity_np ,
.Nm pthread_attr_setaffinity_np
.Nd manage CPU affinity in thread attribute objects
.Sh LIBRARY
.Lb libpthread
.Sh SYNOPSIS
.In pthread_np.h
.Ft int
.Fn pthread_attr_getaffinity_np "const pthread_attr_t *pattr" "size_t cpusetsize" "cpuset_t *cpusetp"
.Ft int
.Fn pthread_attr_setaffinity_np "pthread_attr_t *pattr" "size_t cpusetsize" "const cpuset_t *cpusetp"
.Sh DESCRIPTION
The
.Fn pthread_attr_getaffinity_np
and
.Fn pthread_attr_setaffinity_np
functions allow the manipulation of sets of CPUs available to the specified thread attribute object.
.Pp
Masks of type
.Ft cpuset_t
are composed using the
.Dv CPU_SET
macros.
If the user-supplied mask is not large enough to fit all of the matching CPUs,
.Fn pthread_attr_getaffinity_np
fails with
.Er ERANGE .
Calls to
.Fn pthread_attr_setaffinity_np
tolerate masks of any size with no restrictions.
.Fn pthread_attr_setaffinity_np
uses the meaningful part of the mask, where the upper bound is
the maximum CPU id present in the system.
If bits for non-existing CPUs are set, calls to
.Fn pthread_attr_setaffinity_np
fail with
.Er EINVAL .
.Pp
The supplied mask should have a size of
.Fa cpusetsize
bytes.
This size is usually provided by calling
.Li sizeof(cpuset_t)
which is ultimately determined by the value of
.Dv CPU_SETSIZE
as defined in
.In sys/cpuset.h .
.Pp
.Fn pthread_attr_getaffinity_np
retrieves the
mask from the thread attribute object specified by
.Fa pattr ,
and stores it in the space provided by
.Fa cpusetp .
.Pp
.Fn pthread_attr_setaffinity_np
sets the mask for the thread attribute object specified by
.Fa pattr
to the value in
.Fa cpusetp .
.Sh RETURN VALUES
If successful, the
.Fn pthread_attr_getaffinity_np
and
.Fn pthread_attr_setaffinity_np
functions will return zero.
Otherwise an error number will be returned
to indicate the error.
.Sh ERRORS
The
.Fn pthread_attr_getaffinity_np
functions will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa pattr
or the attribute specified by it is
.Dv NULL .
.It Bq Er ERANGE
The
.Fa cpusetsize
is too small.
.El
.Pp
The
.Fn pthread_attr_setaffinity_np
function will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa pattr
or the attribute specified by it is
.Dv NULL .
.It Bq Er EINVAL
The
.Fa cpusetp
specified a CPU that was outside the set supported by the kernel.
.It Bq Er ENOMEM
Insufficient memory exists to store the cpuset mask.
.El
.Sh SEE ALSO
.Xr cpuset 1 ,
.Xr cpuset 2 ,
.Xr cpuset_getid 2 ,
.Xr cpuset_setid 2 ,
.Xr pthread_getaffinity_np 3 ,
.Xr pthread_np 3 ,
.Xr pthread_setaffinity_np 3
.Sh STANDARDS
The
.Nm pthread_attr_getaffinity_np
and
.Nm pthread_attr_setaffinity_np
functions are non-standard
.Fx
extensions and may be not available on other operating systems.
.Sh HISTORY
The
.Nm pthread_attr_getaffinity_np
and
.Nm pthread_attr_setaffinity_np
functions first appeared in
.Fx 7.2 .
.Sh AUTHORS
.An -nosplit
The
.Nm pthread_attr_getaffinity_np
and
.Nm pthread_attr_setaffinity_np
functions were written by
.An David Xu Aq Mt davidxu@FreeBSD.org ,
and this manpage was written by
.An Xin LI Aq Mt delphij@FreeBSD.org .
